The present project examines the drug and hormone sensitivity of the resistance arterioles (100-400 micrometers, i.d.) supplying individual exchange villi of the human fetal placenta. This study is performed in-vitro using helically cut strips of villus stem arterioles suspended in Krebs-Henseleit bicarbonate buffer equilibrated with appropriate gas mixtures at 37 degrees. Initially, strips of these arteries will be examined for their contractile responses to various vasoactive stimuli under high (600 torr) O2 and under low (approximately 20 torr) O2 conditions to determine if these arterioles respond to alterations in the oxygen levels surrounding the blood vessel wall. These studies will be repeated in blood vessels obtained from placentas from patients with gestational hypertension pre-eclampsia and eclampsia and especially those delivering growth retarded infants. Results of this study will therefore be compred to those results from normal placentas to identify any possible alterations in vascular reactivity which might accompany maternal hypertension and give potential clues as to the mechanism responsible for intrauterine growth retardation. In addition to the studies on the human placental vasculature, numerous similar experiments will be carried out in various experimental animal models commonly used to study pregnancy and/or fetal development. These include the sheep, rabbit and guinea pig in which the uterine (maternal) side of the placental vasculature as well as the fetal side will be investigated. The object of the final phase is to (a) evaluate the species differences in fetal placental vascular sensitivity to vasoactive stimuli and (b) to evaluate the fetal versus maternal vasculatures to similar stimuli.